1. Field of the Invention
The present invention relates to an image forming apparatus including a transfer device for transferring a toner image from an image bearing member toward a belt, and more particularly, to an apparatus in which a transfer device rubs a belt.
2. Description of the Related Art
Conventionally, in an electrophotographic image forming apparatus, there is known a configuration in which a toner image borne by a photosensitive drum as an image bearing member is electrostatically transferred to an intermediate transfer belt by a transfer device to which a voltage of an opposite polarity to that of a charged toner is applied. There is also known a configuration in which a toner image is electrostatically transferred to a recording material borne by a recording material bearing belt. Such transfer device as described above include a transfer device rotating together with a belt, such as a transfer roller which is connected to a high voltage power supply circuit and which is disposed at a location opposed to a photosensitive drum via the belt.
FIG. 16 illustrates an exemplary nip configuration formed between a photosensitive drum and a transfer roller which are opposed to each other with a belt sandwiched therebetween. When a transfer roller is used as a transfer device, there may be cases in which, because the transfer roller rotates, a width of a contact region between the belt and the transfer roller in a movement direction of the belt (so-called transfer nip) changes. This is because the diameter of the transfer roller is not uniform in a strict sense. Therefore, when a toner image is transferred from the photosensitive drum, a current which passes from the transfer roller to the photosensitive drum may change to cause unevenness in transfer.
As a measure against these, Japanese Patent Application Laid-Open No. H05-127546 proposes a configuration in which a brush is used as a transfer member that does not rotate. In such a configuration using a brush, each fiber forming the brush can be independently brought into contact with the belt.
Japanese Patent Application Laid-Open No. H09-120218 discloses a configuration which does not include a belt but uses as a transfer device a film supported by a support member. Further, Japanese Patent Application Laid-Open No. H09-230709 discloses a configuration in which a blade supported by a support member is used as a transfer device.
However, the brush is not brought into contact in a sheet-like manner, and hence unevenness in transfer is liable to occur. Further, with regard to the above-mentioned conventional film as a transfer device which is brought into contact with a rotating belt, a friction force on a contact surface between the transfer device and the belt becomes larger. Therefore, drive torque of the belt with respect to the transfer device becomes larger, and unusual noise may be generated because the transfer device rubs the belt. Further, the friction of a transfer device which rubs the belt is larger than the friction of a rotating transfer roller with a belt, and hence the drive torque for rotating the belt becomes larger, and a load to a drive motor and the like becomes higher.